--- /dev/null
+#ifndef INCLUDED_IMF_RGBA_YCA_H
+#define INCLUDED_IMF_RGBA_YCA_H
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2004, Industrial Light & Magic, a division of Lucasfilm
+// Entertainment Company Ltd. Portions contributed and copyright held by
+// others as indicated. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above
+// copyright notice, this list of conditions and the following
+// disclaimer.
+//
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following
+// disclaimer in the documentation and/or other materials provided with
+// the distribution.
+//
+// * Neither the name of Industrial Light & Magic nor the names of
+// any other contributors to this software may be used to endorse or
+// promote products derived from this software without specific prior
+// written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//////////////////////////////////////////////////////////////////////////////
+
+//-----------------------------------------------------------------------------
+//
+// Conversion between RGBA (red, green, blue alpha)
+// and YCA (luminance, subsampled chroma, alpha) data:
+//
+// Luminance, Y, is computed as a weighted sum of R, G, and B:
+//
+// Y = yw.x * R + yw.y * G + yw.z * B
+//
+// Function computeYw() computes a set of RGB-to-Y weights, yw,
+// from a set of primary and white point chromaticities.
+//
+// Chroma, C, consists of two components, RY and BY:
+//
+// RY = (R - Y) / Y
+// BY = (B - Y) / Y
+//
+// For efficiency, the x and y subsampling rates for chroma are
+// hardwired to 2, and the chroma subsampling and reconstruction
+// filters are fixed 27-pixel wide windowed sinc functions.
+//
+// Starting with an image that has RGBA data for all pixels,
+//
+// RGBA RGBA RGBA RGBA ... RGBA RGBA
+// RGBA RGBA RGBA RGBA ... RGBA RGBA
+// RGBA RGBA RGBA RGBA ... RGBA RGBA
+// RGBA RGBA RGBA RGBA ... RGBA RGBA
+// ...
+// RGBA RGBA RGBA RGBA ... RGBA RGBA
+// RGBA RGBA RGBA RGBA ... RGBA RGBA
+//
+// function RGBAtoYCA() converts the pixels to YCA format:
+//
+// YCA YCA YCA YCA ... YCA YCA
+// YCA YCA YCA YCA ... YCA YCA
+// YCA YCA YCA YCA ... YCA YCA
+// YCA YCA YCA YCA ... YCA YCA
+// ...
+// YCA YCA YCA YCA ... YCA YCA
+// YCA YCA YCA YCA ... YCA YCA
+//
+// Next, decimateChomaHoriz() eliminates the chroma values from
+// the odd-numbered pixels in every scan line:
+//
+// YCA YA YCA YA ... YCA YA
+// YCA YA YCA YA ... YCA YA
+// YCA YA YCA YA ... YCA YA
+// YCA YA YCA YA ... YCA YA
+// ...
+// YCA YA YCA YA ... YCA YA
+// YCA YA YCA YA ... YCA YA
+//
+// decimateChromaVert() eliminates all chroma values from the
+// odd-numbered scan lines:
+//
+// YCA YA YCA YA ... YCA YA
+// YA YA YA YA ... YA YA
+// YCA YA YCA YA ... YCA YA
+// YA YA YA YA ... YA YA
+// ...
+// YCA YA YCA YA ... YCA YA
+// YA YA YA YA ... YA YA
+//
+// Finally, roundYCA() reduces the precision of the luminance
+// and chroma values so that the pixel data shrink more when
+// they are saved in a compressed file.
+//
+// The output of roundYCA() can be converted back to a set
+// of RGBA pixel data that is visually very similar to the
+// original RGBA image, by calling reconstructChromaHoriz(),
+// reconstructChromaVert(), YCAtoRGBA(), and finally
+// fixSaturation().
+//
+//-----------------------------------------------------------------------------
+
+#include <ImfRgba.h>
+#include <ImfChromaticities.h>
+
+namespace Imf {
+namespace RgbaYca {
+
+
+//
+// Width of the chroma subsampling and reconstruction filters
+//
+
+static const int N = 27;
+static const int N2 = N / 2;
+
+
+//
+// Convert a set of primary chromaticities into a set of weighting
+// factors for computing a pixels's luminance, Y, from R, G and B
+//
+
+Imath::V3f computeYw (const Chromaticities &cr);
+
+
+//
+// Convert an array of n RGBA pixels, rgbaIn, to YCA (luminance/chroma/alpha):
+//
+// ycaOut[i].g = Y (rgbaIn[i]);
+// ycaOut[i].r = RY (rgbaIn[i]);
+// ycaOut[i].b = BY (rgbaIn[i]);
+// ycaOut[i].a = aIsValid? rgbaIn[i].a: 1
+//
+// yw is a set of RGB-to-Y weighting factors, as computed by computeYw().
+//
+
+void RGBAtoYCA (const Imath::V3f &yw,
+ int n,
+ bool aIsValid,
+ const Rgba rgbaIn[/*n*/],
+ Rgba ycaOut[/*n*/]);
+
+//
+// Perform horizontal low-pass filtering and subsampling of
+// the chroma channels of an array of n pixels. In order
+// to avoid indexing off the ends of the input array during
+// low-pass filtering, ycaIn must have N2 extra pixels at
+// both ends. Before calling decimateChromaHoriz(), the extra
+// pixels should be filled with copies of the first and last
+// "real" input pixel.
+//
+
+void decimateChromaHoriz (int n,
+ const Rgba ycaIn[/*n+N-1*/],
+ Rgba ycaOut[/*n*/]);
+
+//
+// Perform vertical chroma channel low-pass filtering and subsampling.
+// N scan lines of input pixels are combined into a single scan line
+// of output pixels.
+//
+
+void decimateChromaVert (int n,
+ const Rgba * const ycaIn[N],
+ Rgba ycaOut[/*n*/]);
+
+//
+// Round the luminance and chroma channels of an array of YCA
+// pixels that has already been filtered and subsampled.
+// The signifcands of the pixels' luminance and chroma values
+// are rounded to roundY and roundC bits respectively.
+//
+
+void roundYCA (int n,
+ unsigned int roundY,
+ unsigned int roundC,
+ const Rgba ycaIn[/*n*/],
+ Rgba ycaOut[/*n*/]);
+
+//
+// For a scan line that has valid chroma data only for every other pixel,
+// reconstruct the missing chroma values.
+//
+
+void reconstructChromaHoriz (int n,
+ const Rgba ycaIn[/*n+N-1*/],
+ Rgba ycaOut[/*n*/]);
+
+//
+// For a scan line that has only luminance and no valid chroma data,
+// reconstruct chroma from the surronding N scan lines.
+//
+
+void reconstructChromaVert (int n,
+ const Rgba * const ycaIn[N],
+ Rgba ycaOut[/*n*/]);
+
+//
+// Convert an array of n YCA (luminance/chroma/alpha) pixels to RGBA.
+// This function is the inverse of RGBAtoYCA().
+// yw is a set of RGB-to-Y weighting factors, as computed by computeYw().
+//
+
+void YCAtoRGBA (const Imath::V3f &yw,
+ int n,
+ const Rgba ycaIn[/*n*/],
+ Rgba rgbaOut[/*n*/]);
+
+//
+// Eliminate super-saturated pixels:
+//
+// Converting an image from RGBA to YCA, low-pass filtering chroma,
+// and converting the result back to RGBA can produce pixels with
+// super-saturated colors, where one or two of the RGB components
+// become zero or negative. (The low-pass and reconstruction filters
+// introduce some amount of ringing into the chroma components.
+// This can lead to negative RGB values near high-contrast edges.)
+//
+// The fixSaturation() function finds super-saturated pixels and
+// corrects them by desaturating their colors while maintaining
+// their luminance. fixSaturation() takes three adjacent input
+// scan lines, rgbaIn[0], rgbaIn[1], rgbaIn[2], adjusts the
+// saturation of rgbaIn[1], and stores the result in rgbaOut.
+//
+
+void fixSaturation (const Imath::V3f &yw,
+ int n,
+ const Rgba * const rgbaIn[3],
+ Rgba rgbaOut[/*n*/]);
+
+} // namespace RgbaYca
+} // namespace Imf
+
+#endif
projects / opencv / blobdiff